I. Field of the Invention
The present invention is directed generally to a field of health care that involves monitoring the physiological state of patients with acute or chronic conditions or chronic disease states which predominantly derive decided prognosis advantages from intensive condition tracking. More particularly, the invention is directed to a condition monitoring system which includes one or more remote modular testing units and a central station. The remote units include physiological parameter testing modules to acquire data from one or possibly many patients and communicate with a central station typically capable of interfacing with a large number of patient-operated units or clinician-operated units testing many patients. The central station, in turn, may interface and communicate with any number of other devices as by networking. Parameters checked may include but are not limited to blood pressure, pulse rate, blood oxygen saturation, weight, blood glucose, temperature, prothrombin (clotting) time and pulmonary function, including respiratory rate and depth. Other functions, such as ECG (electrocardiograph) traces and infant breathing monitoring for detection of SIDS (sudden infant death syndrome) onset are also contemplated.
II. Related Art
Patients exhibiting any of a variety of serious, chronic conditions which require monitoring of medications, or the like, benefit from frequent testing. Many conditions which have traditionally required weekly or even daily clinic visits for testing may be tracked using remote monitoring with a customized testing frequency employed. This approach generally exceeds the benefits of care offered by frequent clinic visits at a fraction of the cost. In addition, hospital, assisted living and hospice units, for example, can also benefit greatly from portable, multiple-test patient monitoring units that monitor vital signs and conduct other tests and which are integrated into one management system including a central monitoring system capable of interfacing with many other devices.
An example of such a condition is congestive heart failure (CHE), a major public health concern, presently affecting 2 million patients within the United States. The problem is increasing and is responsible for over 1 million hospitalizations, with a typical length of stay of about six days, every year along with many physician visits. In addition, CHF commonly requires recurrent hospital admissions with 90-day readmission rates of over 50% reported in patients over the age of 70. Factors associated with high admission rates include inadequate follow up, failure of patients to promptly seek medical attention when symptoms recur, and non-compliance with diet and medication regimens. Much of this can be traced to the inadequacy of traditional home care, i.e., the lack of daily involvement of or interaction with the caregiver. The practicality of such situations invites inadequate monitoring of physiological parameters and a failure to appreciate and evaluate drug regimens which may result in inappropriate dosing or adverse side-effects or other problems.
The severity of CHF in an individual can further be evaluated and treatment updated quickly and in an ongoing manner by remote monitoring of several physiological parameters. The basic pathophysiology of CHF is reduced cardiac output usually with increased left ventricular filling pressures. An assessment of arterial pressure and pulse rates can indicate a failing heart. Typically, in patients with CHF, as stroke volume falls, resting heart rate increases. In addition, reduced cardiac output associated with increased pulmonary capillary wedge pressure leads to pulmonary edema and reduced systemic arterial oxygen saturation which is usually manifested as dyspnea by the patient.
Pulse oximetry is now a well-developed and widely used noninvasive technique of assessing oxygen saturation in pulmonary and cardiac patients. The valuable data obtained, including heart rate, has stimulated its use in acute, as well as chronic, care facilities treating pulmonary and cardiac diseases. Pulse oximetry can be used to indicate early signs of worsening cardiac failure if used to monitor patient desaturation during sleep. As left ventricular failure worsens, pulmonary congestion worsens and gas exchange is increasingly impaired, leading to a decrease in the arterial oxygen saturation as well as increase in heart rate. Timely reversal of this condition by relieving the left ventricle from excess afterload is essential and monitoring pulse oximetry also provides a measure of the improvements in cardiac output and reduction in left ventricular filling pressure that occurs with therapy.
Cardiac failure manifests itself by fluid retention and weight gain. Systemic venous congestion, another condition typical of CHF, is also reflected by salt and water retention which produces weight gain and an inappropriate increase in systemic blood pressure. Chronic systemic hypertension is also often the primary cause of failing heart and kidneys. Thus, closely monitoring patient weight also tracks the congestive state. Complementing this with blood pressure, heart rate and pulse oximetry monitoring provides the heath professional multiple objective measures.
Other such widespread chronic diseases or medical conditions include asthma, for example, for which pulmonary function is assessed by obtaining objective measurements of lung volumes and flow rates produced with maximum respiratory effort. These measurements are normally obtained using a spirometer, which measures vital capacity, tidal volume, expiratory reserve volume, and inspiratory capacity. Spirometry is an accepted, direct and sensitive measure of respiratory status that provides data for the direct assessment of current health status, disease exacerbation, compliance with prescribed drugs and drug efficacy.
Clinical experience has also shown that having patients perform Peak Expiratory Flow Rate (PEFR) measurements improves the clinician's ability to provide effective treatment.
Some reported uses of home PEFR are:
(1) monitoring to detect early airway obstructions and initiate timely therapy.
(2) monitoring the course of treatment, using objective criteria to alter steps in the treatment plan.
(3) determining when emergency medical care is needed.
(4) providing feedback to help patients perceive the severity of their obstruction.
Presently, PEFR is the only measurement obtained at home by patients using a Peak Flow Meter. However, the spirometer measures, along with PEFR, Forced Vital Capacity (FVC), Forced, Expiratory Volume at One Second (FEV.sub.1), and Forced Expiratory Flow between 25% and 75% of the curve (FEF.sub.25/75). These measurements require no additional effort by the patient yet they provide significantly more diagnostic information than the Peak Flow Meter.
Between 12 and 13 million people in the United States have diabetes mellitus and each year an additional 500,000 to 700,000 people are diagnosed with diabetes, of which 5% to 10% are diagnosed to have Insulin Dependent Diabetes Mellitus (IDDM). Patients diagnosed with IDDM must regularly inject themselves with insulin and monitor their blood glucose level with a glucose meter. A recent federal government study completed in 1993 has proven that lowering blood glucose levels to the normal range reduces the risk of major complications, such as blindness, kidney failure, heart attack or amputation and had reinforced the need for intensive management or close monitoring of diabetic patients. Intensive management may involve testing blood sugar level several times a day, at considerable expense and inconvenience, clearly avoidable by telecommunication glucose monitoring.
The above and other conditions reflect a growing need for remote patient monitoring. Some monitors have been developed for recording and transmitting certain patient-related information between remote locations and central stations or physicians, offices.
U.S. Pat. No. 4,803,625, issued to Fu et al, for example, discloses a portable patient unit connected to a central unit via a telephone line. The portable patient unit includes sensors for weight, temperature, blood pressure and ECG waveforms and may prompt the patient to take medicine, to use the sensors and to supply answers to various questions. The system allows communication between the patient unit and a central station and also can be used to query the patient where discrepancies between measured and expected values exist in the data.
U.S. Pat. No. 4,838,275, issued to Lee, which describes a home medical surveillance system that includes a large number of patient subscriber apparatuses that interface with a central station. Data is taken at a particular predetermined time and transmitted directly to the central station from the patient when taken. Parameters monitored may cover a broad spectrum and include blood pressure, heart rate, ECG, respiration rate and depth, center of gravity shifts, weight, temperature, breathing sounds, shivering, conversational characteristics, average blood glucose and relative cardiac output. The central office or station includes devices for transmitting/receiving interaction between the subscribers and the central station.
Gallant et al, U.S. Pat. No. 5,231,001, describes a microprocessor-based ambulatory patient monitoring system which may use a plurality of devices for measuring such parameters as ECG, blood pressure, oxygen saturation, temperature and respiratory function. Some degree of modularity is contemplated with the monitoring units. Data may be transmitted from the monitoring units over the telephone line to a PC. An optical interface may coordinate operation of one or more of the measuring units. The monitoring units may be coupled to a central computer system also utilized by the physician when particular patient information is relevant to identifying the patient and the data collected is relevant to any particularly measurement protocols, operating parameters and event triggering data.
U.S. Pat. No. 5,012,411, to Policastro et al, further describes a portable microprocessor-controlled apparatus for monitoring, storing and transmitting blood pressure, flow, and brain wave data from stored memory to a remote location over a telephone line or to a built-in graphic display or printer.
It remains, however, that the known remote patient monitoring devices or combinations of devices are relatively inflexible, generally dedicated to monitor particular conditions. They have varying degrees of portability and interface abilities both with the patient and with a remote monitoring station. There remains a definite need to provide a modular remote patient monitoring system which includes an interactive central station and self-contained mobile remote patient units, each of which can be tailored by the medical professional to perform measurements related to particular conditions applicable to each patient of interest. Interchangeable modular measurement parameter devices associated with a single, completely mobile patient monitoring unit adds a degree of control and flexibility not found in present systems.